Accoustical tape loop sensor

ABSTRACT

A pulsed ultrasonic ranging system may be used to sense the position and velocity of tape in a vacuum buffer column. The received pulses may be stored in an accumulator to provide position information whereas the value of successive accumulations can be used to indicate velocity. A single piezoelectric transducer can be used as both transmitter and receiver.

United States Patent 1 1 Buchan et al.

[ 1 Nov. 6, 1973 [5 ACCOUSTICAL TAPE LOOP SENSOR 3,673,553 6/1972 Miuraet al. 340/5 8 e [75] Inventors: William Arthur Buchan, El Toro, ggfiggg1971 cfimp R [1962 K1etzetal.... 340/3 R Q l ph R 3 M1 5 3,047,1937/1962 Long 226/42 VICJO, Callf. [73] Assignee: L a g stems PrimaryExaminer-Richard A. Farley a] Attorney-John A. Duffy et al. [22] Filed:Nov. 11, 1971 21 A I. No.: 197 867 l 1 pp 57 ABSTRACT [52] U.S. Cl.340/1 R, 226/42, 2.26/45, A pulsed ultrasonic ranging system may be usedto 340/5 S sense the position and velocity of tape in a vacuum [51] Int.Cl. G0ls 9/68 buffer column. The received pulses may be stored in an[58] Field of Search 226/29, 30, 42, 43, accumulator to provide positioninformation whereas 226/45; 340/1 R, l L, 1 T, 259, 260, 3 R, 5 S, thevalue of successive accumulations can be used to 16 C; 18 l/0.5 NPindicate velocity. A single piezo-electric transducer can be used asboth transmitter and receiver. [56] References Cited UNITED STATESPATENTS 1 Claim, 8 Drawing Figures 2,743,429 4/l956 Erdman et al. 340/lR re4w9M/r p g' y /7[ 726? fid5/770/t/ 1 av; y 1 57/07" [7U H2 71?VZfif/T/ 1 ACCOUSTICAL TAPE LOOP SENSOR BACKGROUND OF THE INVENTION In atypical computer tape system, the high inertia storage reels areisolated from one another by buffer vacuum columns. These columns arespaced on either side of a capstan drive arrangement, and allow the tapeat the capstan to be rapidly stopped and started while the reels followwith lower acceleration rates. In order to effect proper operation ofthe reels, it is necessary to supervise the status of tape in thesecolumns. Numerous devices have been utilized to accomplish this functionsuch as optical sensing, capacitive sensing, pressure sensing, etc. Eachof the prior art solutions to the problem have relative advantages anddisadvantages. For example, the optical system is subject to effects ofambient background lighting; the capacitive system is dependent uponaccurate mechanical characteristics and is affected by vibration andtemperature changes, the pressure system is limited to bang-bang type ofservos (ON-OFF) with the consequent effect of hunting, etc. What isactually desired is a proportional sensing system which is relativelyunaffected by external environmental factors.

Accordingly, a primary object of the present invention is to provide anaccoustical tape loop detecting system.

Another object of the present invention is to provide a system forsensing both the position and velocity of tape in a buffer column.

It is a further object of the present invention to provide aproportional tape loop servo system which is relatively uninfluenced byextraneous environmental changes.

Other objects and advantages of the present invention will be obviousfrom the detailed description of a particular embodiment given hereinbelow.

SUMMARY OF THE INVENTION The invention comprises an ultrasonictransducer which is pulsed to provide transmit signals that arereflected from the tape inside the column. The return signals from thetape are sensed by the same transducer and the echo time is measured bya high frequency digital clock whose pulses are stored in an accumulatorduring the time between the transmit and receive signals. When the echosignal. is received the accumulator contents is a measure of tapeposition. Each accumulator count is stored and the difference betweenthe present accumulator contents and a previous one is used to measuretape velocity. The resultant position and ve locity information are usedas inputs to the reel servos.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows a typical buffered tapetransport.

FIG. 2 shows the physical arrangement of the accoustical sensor relativeto the tape column.

FIG. 3 shows the timing waveforms between TRANS- MI'I'IED and RECEIVEDsignals.

FIG. 4 shows a block diagram of a digital circuit embodiment of theinvention.

FIG. 5 shows the waveforms associated with the elements shown in FIG. 4.

FIG. 6 shows the crystal excitation and reception circuitry.

FIG. 7 is a block diagram of. an analog embodiment of the invention.

FIG. 8 shows the waveforms associated with the elements shown in FIG. 7.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Adverting to the drawingsand particularly FIG. 1, a typical buffered loop tape transportcomprises a pair of reels l0 and 11, a capstan 12, a read-write headassembly l3 and a pair of vacuum columns 14 and 15. The position of thetape 16 in a vacuum column (for example column 14) is maintained by aservo system which drives the reel 10 so as to bring the loop to somepreestablished null (normally near the physical center of the column).In the present invention, the signal which controls the servo is derivedfrom the accoustical sensing arrangement shown in FIG. 2. In thissystem, a piezo-electric transducer 17 is mounted in the floor 18 of thecolumn and used to generate an ultrasonic pulse which is reflected fromthe tape 16. The return signal is detected by the same transducer 17 andthe time lapse t between the transmitted signal and the echo determinesthe distance L between the transducer 17 and the tape 16, i.e.,

where v, velocity of sound in the low pressure area beneath the tape.

FIG. 3 shows a timing diagram of transmitted and received pulses. Duringthe duration t,, of the driving pulse [line (1)] the piezo-electriccrystal 17 is driven at its resonant frequency to produce theoscillatory waveform shown as the transmitted pulse [line (2)]. Uponreturn, the echo causes the piezo-electric crystal to vibrate at itsresonant frequency producing the electrical voltage shown on line (3).This voltage is amplified and used to trigger an electronic circuit(such as a one shot multi-vibration) whose output is indicated on line(4).

FIG. 4 shoes a block diagram of the requisite circuitry for practicingthe invention. The corresponding waveforms are shown in FIG. 5. Theoperation of the system is as follows: The clock generator 20 producespulses every 20 psec as shown in FIG. 5 (CLOCK). The output of the clockgenerator 20 is divided down by the frequency divider 21 to produce atransmit pulse every 6 milliseconds FIG. 5 [Xmit]. At the time of TRANS-MIT, the accumulator 22 is enabled (line 23) and counts clock pulses(line 24) until a RECEIVE pulse arrives (line 25). At this time thecontents of the accumulator [FIG. S-accum] are a measure of the length L(FIG. 2). The timing logic 26 responds to the receive pulse andgenerates the appropriate subtract, transfer and reset pulses asindicated. The subtract pulse (line 27) causes the contents stored fromthe previous accumulator (located in memory 31) to be subtracted fromthe present accumulator content. This is accomplished by the subtractor28. This difference is the velocity (line 29). The transfer'pulse (line30) causes the present contents of the accumulator to be transferred tostore (memory 31). The reset pulse (line 32) resets the accumulator 22to zero in readiness for the next TRANSMIT RECEIVE cycle. Thecorresponding waveforms for successive accumulator values of 4.5, 4 and3.5 units are illustrated on line (7) (10) of FIG. 5.

FIG. 7 shows a typical circuit for driving the piezoelectric crystal.The return wave causes the crystal to vibrate at its resonant frequencyproducing an electrical output which amplified (amplifier 40) anddetected (threshold detector 41) to produce an electrical pulse on line42.

An analog embodiment (and the associated waveforms) of the invention isshown in FIGS. 7 and 8 respectively. In this system, the transmit pulsesets a flip flop to one state and the receive pulse sets it to theopposite state. The filtered output is a voltage whose amplitude isproportional to position. Alternate RE- CEIVE pulses are also used totrigger a one shot whose pulse width is equal to the time betweenTRANSMIT PULSES. The phase difference between the trailing edge of theone shot and the next RE- CElVE pulse is a measure of velocity. Thisphase difference is detected by the phase detector and the output isfiltered to provide a voltage proportional to velocity.

It will be obvious of course, that what has been said with respect tosensing the tape in one column is equally applicable to sensing tape inthe other column. It should also be evident that the basic concept ofthe invention is not limited to magnetic tape or buffer columns ingeneral but is equally applicable to numerous sound ranging systems suchas safety devices, reare'nd collision vehicle warning devices, etc. Noris the invention limited to the particular arrangement of componentsshown herein it being understood that the particular embodiment was usedfor exemplary purthe spirit of the invention.

We claim: 1 A system for supervising tape in a bufier column comprising:

means for transmitting an acoustical signal within a tape buffer column;means for'sensing an echo signal reflected from the tape in the buffercolumn; means for measuring the time between the transmitted signal andthe echo signal whereby the position of the tape may be determined, saidtime measuring means comprising: a flip flop;

means for setting said flip flop to a first state at the time a signalis transmitted; and means for setting said flip flop to its oppositestate at the time a signal is received, whereby the average value of theoutput of said flip flop is a representation of the time betweentransmitted and received signals, and wherein is a, means for measuringthe velocity of the tape in the column, said velocity measuring meanscomprising: detection means responsive to alternate echo signals; a oneshot multivibrator responsively connected to said detection means, saidone shot having a period equal to the time between transmit signals;means for detecting the phase difference between the time at which saidone shot returns to its stable state and the time at which an echosignal is received.

l l l I!

1. A system for supervising tape in a buffer column comprising: meansfor transmitting an acoustical signal within a tape buffer column; meansfor sensing an echo signal reflected from the tape in the buffer column;means for measuring the time between the transmitted signal and the echosignal whereby the position of the tape may be determined, said timemeasuring means comprising: a flip flop; means for setting said flipflop to a first state at the time a signal is transmitted; and means forsetting said flip flop to its opposite state at the time a signal isreceived, whereby the average value of the output of said flip flop is arepresentation of the time between transmitted and received signals, andwherein is a, means for measuring the velocity of the tape in thecolumn, said velocity measuring means comprising: detection meansresponsive to alternate echo signals; a one shot multivibratorresponsively connected to said detection means, said one shot having aperiod equal to the time between transmit signals; means for detectingthe phase difference between the time at which said one shot returns toits stable state and the time at which an echo signal is received.